Field of the Invention
The present invention relates, in general, to a voltage synchronization method and system, and, more particularly, to a voltage synchronization method and system which can synchronize voltage values by reducing differences between the voltage values that are respectively sensed by controllers.
Description of the Related Art
Voltage sensing controllers connected to a high-voltage line of a fuel cell vehicle (FCV) include a stack voltage monitoring device (SVM), a motor control unit (MCU), a power converter controller (PCC), a blower/pump control unit (BPCU), etc. When a fuel cell control unit (FCU) for overall operation of a FCV transmits a voltage command for the recovery of regenerative braking energy to a PCC, the PCC may be configured to store the energy in a high-voltage battery through power control in response to the voltage command. However, when the control voltage of the PPC is less than a voltage sensed by an MCU, the torque for regenerative braking is reduced due to a voltage upper limit constraint and the intended amount of energy may be not stored.
In addition, when a FCV slips back on a slope while starting from a stopped state, regenerative braking may occur as a motor rotates in the reverse direction. When the voltage sensed by the MCU is greater that the voltage of PCC by a specific offset value, the size of the voltage sensed by the MCU is increased by regenerative braking. When a maximum voltage value at which regenerative braking is no longer possible is reached, the motor is derated. The voltage value sensed by the MCU is decreased during the derating of the motor and increases due to subsequent regenerative braking and then deration occurs again. As these processes are repeated, the problem of the FCV being subjected to substantially heavy vibration occurs. This problem occurs due to the difference between the voltage sizes sensed by the PCC and the MCU in response to the voltage command that the FCU transmits to the PCC. To correct the different sizes of voltages, calibration is performed in consideration of errors in voltage sensors of the MCU and the PCC at the time of the development of the MCU and the PCC. However, voltage sensors designed for separate parts, such as the MCU and the PCC, have different errors. When the MCU and PCC are coupled to a high-voltage line, the voltage sizes sensed by the separate parts are different.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.